1. Field of the Invention
The present invention relates to a filter, and more particularly, to a tracking filter for selecting a channel of a wideband frequency.
2. Background of the Related Art
Since there are 120 TV channel signals mixed together in a wide band, signal interference between adjacent channels becomes an issue.
To solve such an issue, a variety of methods such as a double conversion tuner method and a single conversion tuner method exist.
Here, the single conversion tuner comprises a tracking filter.
That is, the linearity of the tuner can be improved by comprising a tracking filter in the tuner so as to perform a channel selection.
Among such single conversion tuners, there is a 3-band division tuner of Infineon Technologies as one of the recently developed techniques.
FIG. 1 is a block diagram of a conventional 3-band division tuner.
The conventional 3-band division tuner depicted FIG. 1 illustrates a schematic block diagram of a tuner of Infineon Inc. The 3-band division tuner 100 comprises a tracking filter 101 for channel selection.
Here, the tracking filter 101 serves as a filter for tracking a 3-band frequency.
The 3-band indicates a VHFL frequency band of about 57 to 159 MHz, a VHFH frequency band of about 165 to 453 MHz and a UHF frequency band of about 459 to 861 MHz.
That is, since there is no a switching structure for channel selection in the conventional 3-band division tuner, the characteristics of a resonator, the tracking performance and the image rejection performance of the conventional 3-band division tuner are enhanced as compared to the existing 2-band (VHF/UHF) receiver.
The power consumption of the conventional 3-band division tuner becomes lower than that of a double conversion tuner, and it can be suitably used in a mobile communication terminal or portable terminal.
However, the 3-band division tuner 100 of Infineon Inc. is disadvantageous in that a high sensitivity (high-Q) air coil LC filter should be provided on the outside thereof and a high voltage, approximately 20V, should be applied to an external varactor for tuning the frequency.
Further, there is a drawback that the tuning of the tuner should be done by manual works, which makes it not appropriate for mass production. And, due to the air coil LC filter on the outside, the outer profile of the 3-band division tuner 100 becomes bigger.